1. Field of the Invention
The present invention relates to an optical disk drive apparatus, and particularly relates to an optical disk drive apparatus capable of performing calibration.
2. Description of the Related Art
Optical disk devices of a recordable-type device may be categorized into a Write-Once type and an Erasable type. There are several recording methods for the Write-Once type optical disk. One method is to dispose a material such as Tellurium (Te) or Bismuth (Bi) on a signal-recording surface of the optical disk and then irradiate a laser beam on the recording surface so as to melt the material and form pits thereon. Another method is to utilize a thin-layer of Sb2Se3, TeOx or an organic dye as a material of a recording surface and then irradiate a laser beam on the recording surface to vary the light reflectivity.
CD-R disk is one of the Write-Once type optical disks which is provided with pregrooves for guiding purpose. The pregrooves are provided in a slightly wobbled manner in a radial direction with a central frequency of 22.05 kHz. The pregrooves are provided with address information called ATIP (Absolute Time In Pregroove) recorded thereon in a multiplexed manner by FSK modulation with a maximum deviation of +/−1 kHz.
FIG. 1 is a diagram showing a signal-recording format of a CD-R disk. As shown in the figure, the signal recording format of the CD-R disk includes a power calibration area (PCA) provided at a location closer to the center of the disk for recording and measuring an optimum recording power and an information area provided at an outer location. The information area includes a program memory area (PMA) for temporarily storing signal-recording information or skipping information during a Write-Once operation, a read-in area, a user data area and a read-out area.
In case of the CD-R disk which is a write-once type optical disk, an OPC (Optimum Power Control) operation is carried out prior to actual recording of the information, in order to determine an optimum recording power of the laser beam. The OPC operation is an operation for measuring recording characteristics and is carried out on the power calibration area provided at a predetermined position of the disk.
The power calibration area includes a test area for 100 tests (partitions: P100-P001). Each partition includes 15 frames (F01-F15). Test signals are recorded into each one of the 15 frames at 15 different levels of recording power and the test signals recorded in the frames are reproduced individually. A peak value and a bottom value of the test signal are detected for each frame. The optimum recording power is determined based on the peak values and the bottom values. Among the 15 steps of recording power, a recording power that exceeds a predetermined value is selected as the most suitable recording power, i.e., an optimum recording power, for carrying out the following recording operation. Note that it is necessary to select the optimum recording power in such a manner since recording characteristics of the disks differ between different disk manufacturers. If the optimum recording power of the disk is not obtained, the reproduced signals may be reproduced with an increased jitter and at a higher error rate.
FIG. 2 is a graph illustrating a waveform of an AC-coupled RF (high-frequency) signal obtained by reproducing signals recorded on a CD-R disk for showing a peak value (P) and a bottom value (B) of an envelope of the AC-couple RF signal. The AC-coupled RF signal is obtained by removing DC components from the reproduced signals, and thus only contains alternating current (AC) components.
In the prior art, one level of recording power is assigned to each frame and a recording operation is carried out on the test area at 15 steps of power between the minimum level of power and the maximum level of power. Then, as shown in FIG. 2, the peak value (P) and the bottom value (B) of the envelope of the AC-coupled RF (high-frequency) signal reproduced from the test area are detected. A characteristic value for each level of the recording power may be expressed as:characteristic value β=(P+B)/(P−B).If the bottom value (B) takes a negative value and has the same magnitude as the peak value (P), it holds that: P+B=0, resulting in that β=0. When the characteristic value β=0, it may be regarded that the peak value (P) and the bottom value (B) are symmetrical about the horizontal axis. Then, a recording power level for a state where the characteristic value β exceeds a predetermined value (for example, 0.04) is taken as an optimum recording power. Subsequent signal recording is carried out based on the thus-obtained optimum recording power.
In the prior art, since the rotational speed of the optical disk is relatively low, even if recording and reproducing on the test area of the optical disk is carried out at the same speed, the recording characteristic can be measured without reducing an accuracy of measurement. However, recently, due to an increased rotational speed of the optical disk, it is difficult to obtain sufficient number of samples of the signals reproduced from the test area of the optical disk. Accordingly, it has been proposed to reduce the rotational speed of the optical disk during reproduction, so as to maintain the accuracy of measurement of the recording characteristic.
However, in a method which maintains the accuracy of measuring the recording characteristic by reducing the rotational speed of the optical disk, the rotational speed of the optical disk must be reduced from a higher speed to a lower speed. Therefore, there is a problem that a greater load is applied to the optical disk drive apparatus and thus the life of the optical disk drive apparatus becomes shorter.
Also, as has been described above, when it is necessary to perform an operation of reducing the rotational speed from a higher speed to a lower speed, there is a problem that an OPC operation becomes time-consuming.